When grinding cylindrical work pieces with through-feed in a centerless grinding machine, the axial feed of the work pieces is carried out by the fact that the axis of the regulating wheel is inclined in relation to the axis of the grinding wheel, whereby an axial force component from the regulating wheel acts on the work pieces. In order to maintain a sufficient coefficient of friction between the regulating wheel and the work pieces and to maintain a suitable shape of the regulating wheel, the regulating wheel is dressed from time to time, whereby a dressing device, usually comprising a diamond point, is move along the envelope surface of the regulating wheel, thereby removing a surface layer of said wheel. The dressing device is thereby in the most simple manner moved in a path describing a straight line parallel to the feed path describing a straight line parallel to the feed path of the work pieces while the regulating wheel rotates around an axis which is inclined as mentioned above. Such a dressing procedure gives a hyperbolic shape of the regulating wheel envelope surface. It is for various reasons that the work pieces have the longest possible line contact with the regulating wheel, but since the work pieces have cylindrical shape, i,e, they have a certain thickness, line contact can, in theory, not be established between a work piece and a regulating wheel which is shaped according to the above, and the conditions deteriorate with increased work piece diameter.
It is known to compensate for said contact line inaccuracy by increasing the inclination of the regulating wheel after the dressing operation, but this method is impractical because it entails that the inclination of the regulating wheel has to be changed before and after every dressing operation. Another compensation method is to incline the path of the work pieces through the machine, but this method is practicable only for short work pieces and also influences the contact between the grinding wheel and the work pieces. In order to achieve line contact, it is also possible to use a dressing device in the shape of a roller with the same diameter as the work piece. Such a solution is, however, expensive because the cost of each dressing roller is high, and different rollers must be used for different work piece diameters. Further, it would be necessary to provide driving means for the roller in order to make it rotate.
Another solution, which is shown in e.g. the U.S. Pat. No. 2,459,923, is to provide a dressing point on support which is movable along the regulating wheel and let the path of the dressing point be determined by a forming bar with a cylindrical surface which co-operates with a follower connected to the support, whereby in order to adapt to different diameters the bar can be turned in a plane mainly perpendicular to the direction of the pressing force of the follower against the bar. This solution has the disadvantage that the follower has to follow a curve along a surface which is curved in several perpendicular planes when the bar is inclined, which results in oblique load and imperfect forming accuracy in the dressing operation.
It is known to make a forming bar at least partially elastically deformable so that it can be bent by applying one or more forces produced by adjusting screws directed mainly perpendicular to that surface of the bar which defines the path of the dressing point. Such devices are shown in e.g. the Swedish Patent publication No. 314,008, the German Offenlegungsschrift No. 2,153,201 and the U.S. Pat. Nos. 2,073,577 and 2,282,038. It is difficult to give the surface the desired arc shape in such devices. A plurality of adjusting screws are required in order to achieve a variable curve radius and maintained arcuate shape which entails complicated manufacture and handling. If deformation is carried out by only one adjusting screw, the curvature becomes non-circular except possibly regarding bars with flexible parts shaped in a special way at a certain degree of deformation, which entails a limited usefulness and precision. The perpendicular direction of the screws makes it necessary to take up reactive forces.